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IGCSE Physics > P10 Magnetism > Flashcards

P10 Magnetism Flashcards

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1
Q

what is a MAGNETIC FIELD?

A

where a magnet/magnetic material experiences force

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2
Q

examples of MAGNETIC MATERIAL

A

iron, steel, nickel, cobalt

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3
Q

what happens to magnetic materials when they’re next to magnets? why?

A

ATTRACTED because of INDUCED MAGNETISM (domains line up)

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4
Q

how do you DESTROY A MAGNET (remove magnetism)?

A

make the domains point in different directions:

  • hammer it
  • heat it
  • wrap a coil and pass alternating current
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5
Q

why doesn’t a normal piece of magnetic material (e.g. iron) act like a magnet?

A

domains point at different direction and cancel out

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6
Q

how do you MAKE A MAGENT from magnetic material?

A

make the domains line up:

  • stroking
  • put next to another magnet
  • wrap coil + pass current
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7
Q

difference between IRON and STEEL’S MAGNETISM

A

IRON: soft - easy to magnetize and demagnetize (immediately loses magnetism when magnetic field is removed)

STEEL: hard - hard to magnetize and demagnetize (retains magnetism even after magnetic field is removed)

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8
Q

property of INDUCED MAGNETS

A

TEMPORARY MAGNETISM, loses magnetism when magnetic field is removed

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9
Q

how do you SHOW THE DIRECTION of MF?

A

small compasses in a circle → needles point in the direction of field lines

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10
Q

magnetic field lines always go from … to … outside the magnet

A

N to S

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11
Q

DENSER magnetic field lines means…

A

STRONGER magnetic field

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12
Q

uses of HARD magnetic materials

A

making permanent magnets, loudspeaker

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13
Q

uses of SOFT magnetic materials

A

motors, generators, electric bells, transformer cores

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14
Q

differences between ELECTROMAGNETS and PERMANENT MAGNET

A

PERMANENT MAGNET:

  • constant strength of magnetic field
  • can’t be switched on/off
  • N and S can’t be changed

ELECTROMAGNET:

  • variable strength of magnetic field
  • can be quickly switched on/off
  • N and S can be changed by changing direction of current
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15
Q

how do you measure the strength of an electromagnet?

A

measure the mass of paper clips it can hold

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16
Q

do you use iron or steel as the core in the LOUDSPEAKER? why?

A

STEEL cuz its HARD magnetic material - doesn’t lose magnetism easily

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17
Q

do you use iron or steel as the core in the RELAY? why?

A

IRON cuz its SOFT magnetic material - can change magnetism easily

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18
Q

what happens when electric current flows through a wire?

A

MAGNETIC FIELD is created

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19
Q

difference between A.C. and D.C.

A

D.C. → doesn’t change direction → constant MF

A.C. → changes direction → alternating MF

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20
Q

how does the pattern of magnetic field look like outside a SOLENOID?

A

same as bar magnets

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21
Q

how does the pattern of magnetic field look like outside a CURRENT-CARRYING WIRE?

A

circular, perpendicular to wire

22
Q

how do you make an electromagnet stronger?

A

• increase current/voltage
• increase number of turns in coil
→ increased strength of MF

23
Q

how do you determine the DIRECTION OF MF in a CURRENT-CARRYING WIRE?

A

right hand rule:
• thumb - direction of current
• fingers - direction of MF

24
Q

how do you determine the DIRECTION OF MF in a SOLENOID?

A

right hand rule:
• thumb - points to N pole
• fingers - direction of MF

25
Q

explain the MOTOR EFFECT

A

power supply gives VOLTAGE across coil → CURRENT flows through coil → MF induced around coil → INTERACTS with permanent magnet’s MF → interaction creates FORCE → coil spins

26
Q

MOTOR EFFECT:

how to increase the size of force?

A
  • increase current/voltage
  • increase turns of coil
  • stronger magnet → stronger MF
27
Q

MOTOR EFFECT:

how to reverse the direction of force?

A
  • reverse direction of current (battery)

* reverse direction of MF

28
Q

uses of motor effect

A

hairdryer, blender, electric drill, etc.

29
Q

MOTOR EFFECT:

how to determine direction of force/current/MF if others are known?

A

right-hand slap rule:
拇指 - Current
其他手指 - Magnetic Field
手心 - Force

fleming’s left-hand rule:
拇指 - F (force)
食指 - B (magnetic field)
中指 - I (current)

30
Q

energy transfer in D.C. MOTOR

A

electrical → kinetic

31
Q

D.C. MOTOR:

what component is needed? why?

A

SPLIT-RING COMMUTATOR

ensures current always flow the same way → continuous rotation of coil

32
Q

explain the GENERATOR EFFECT (also known as electromagnetic induction)

A

electric conductor experiences CHANGE IN MF → VOLTAGE is induced → CURRENT is generated

33
Q

GENERATOR EFFECT:

explain 2 ways in which you can induce current + observation to show current is induced

A

move a wire (connected to galvanometer) up and down between N and S poles of a magnet → cuts through MF lines → induces V+I → galvanometer needle moves

move a magnet in and out of a coil (connected to galvanometer) → cuts through MF lines → induces V+I → galvanometer needle moves

34
Q

GENERATOR EFFECT:

what device do you use to show current is induced?

A

galvanometer

35
Q

GENERATOR EFFECT:

how to increase the size of induced current?

A
  • faster motion
  • more turns of coil
  • stronger magnet → stronger MF
36
Q

A.C. GENERATOR:

why is an alternating current (a.c.) produced instead of direct current (d.c.) ?

A

one side of the coil moves up → induces VOLTAGE in one direction → induces CURRENT in one direction

… rotation continues …

same side of the coil moves down → induced VOLTAGE reverses direction → induced CURRENT reverses direction

*this repeats and produces a constantly changing current

37
Q

A.C. GENERATOR:

when is the induced V+I at maximum?

A

when coil moves PERPENDICULAR TO MF → cutting MF

38
Q

A.C. GENERATOR:

when is there no induced V+I at all?

A

when coil moves PARALLEL TO MF → not cutting MF

39
Q

A.C. GENERATOR:

what components are needed? why?

A

SLIP RING + BRUSH

maintain contact between coil and external circuit

40
Q

energy transfer in A.C. GENERATOR

A

kinetic → electrical

41
Q

uses of generator effect

A

wind turbines

42
Q

what is the function of a TRANSFORMER?

A

change V to a bigger/smaller value

43
Q

STEP-UP transformer:

function, look, advantage?

A

increases voltage
more coils on secondary side
minimizes energy loss

44
Q

STEP-DOWN transformer:

function, look, advantage?

A

decreases voltage
less coils on secondary side
safe to use

45
Q

why does a STEP-UP transformer MINIMIZE ENERGY LOSS?

A

(constant power, P=IV)

V increase → I decrease → lower I wastes less energy

46
Q

explain how a TRANSFORMER works

A

Alternating Vp → Alternating Ip → Alternating MF
→ Alternating MF induced in iron core
→ Vs is induced → Is flows

47
Q

TRANSFORMER:

what material is the core made of? why?

A

IRON
cuz it is SOFT MAGNETIC MATERIAL
→ can be magnetized (MF can be induced)
→ easy to magnetize and demagnetize

48
Q

TRANSFORMER:

what’s the equation relating V and N (number of coil) on primary and secondary sides?

A

Vp/Np = Vs/Ns

49
Q

TRANSFORMER:

what’s the equation relating V and I on primary and secondary sides?

A

P = Ip• Vp = Is • Vs

50
Q

TRANSFORMER:

what type of current is needed at primary side? why?

A

A.C.

cuz it needs to induce a CHANGING MF

IGCSE Physics (9 decks)

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